Treatment of zinc solutions for the recovery of the metal therefrom.



UNITED STATES PATENT OFFICE.

ROBERT LANCE, OF PARIS, FRANCE.

TREATMENT OF ZINC SOLUTIONS FOR THE RECOVERY OF THE METAL THEREFROM.

No Drawing.

To all whom it may concern:

Be it known that I, Ronnn'r LANCE, a citizen of the French Republic, and residing at 332 Rue Saint-Honor, Paris, France, chemist, have invented certain new and useful Improvements, in and Relating tothe Treatment of Zinc Solutions for'the Recovery of the Metal Therefrom, of which the following is a complete-specification.

This invention has for its object to provide an improved process for the treatment of zinc solutions for the purpose of recoveringthe metal therefrom preferably in the form of oxid.

It has already been proposed for the pur pose of extracting zinc from a solution of zinc sulfate or any other zinc salt, to add to the solution an acid solution of calcium bisulfite. The reaction causes a precipitation of sulfate of lime, the zinc remaining in solutionin the form of bisulfite having separated out the sulfate of lime, the zinc sulfite is precipitated by removing the sulfurous acidwhich keeps it iii solution. This sulfurous acidjoined to the sulfurous acid derivedfrom the calcination of the sulfite, allows of producing anew by known means the acid solution of calcium bisulfite which is used, in the first reaction. The solution, namely the said acid solution of calciu'mdoisulfite is not a chemical combination, but is a solution of calcium sulfite in an aqueous solution of sulfurous acid.

' content in lime as in sulfurous acid is therefore necessarily variable. Since the solubility of zinc sulfite is difi'erent from that of calcium sulfite in the aqueous solution of sulfurous acid, it may happen that the composition of the solution will not allow of maintaining in solution the zinc sulfite produced by the decomposition of the zinc salt by calcium sulfite. In such a case the zinc is precipitated in the form of sulfite in the sulfate of lime. At the same time the zinc solution from which the Zinc is subsequently to be precipitated, is diluted to an extent which is always considerable. For the purpose of obviating this dilution it has already been proposed to modify the process by adding either in the from of .quick lime or in the form of slakcd lime or in the form of carbonate of lime, the quantity of lime which is necessary for fixing the sulfuric acid of the zinc sulfate when the sulfurous acid is subsequently introduced under pressure into the liquor. If lime (quick Specification of Letters Patent.

After I Tts Patented Sept. 12, 1916.

Application filed June 24, 1914. Serial No. 846,995.

lime or slaked lime) is added to the solution of zinc sulfate, and the sulfurous acid isintroduced afterward, then the reaction is limited to the precipitation of the zinc by the lime,

and it is the precipitated hydrated oxid which is then redissolved by the sulfurous acid in excess. The precipitation is however not wholly in the form of'lrvdroxid, and the first portions of hydrated oxid combine with the lime to produce calcium-zincate. On the other hand since the lime is employed in an insoluble-state, the lime particles are immediately coated with a skin of sulfate of lime which being likewise insoluble will very quickly stop the reaction, and the solution of sulfate ofzinc will difi'use with great difiicultythrough the crust of sulfate, which grows thicker and thicker. The action of the balls in the rotary apparatus obviously favors the reaction by crushing the precipitate, but this reaction is nevertheless still slow and incomplete. .It necessitates the use of an additional quantity of lime and occasions a loss ofjzinc in the form of earthy alkaline zincate. 'It, as above stated, the reaction is effected by means of carbonate of lime, the above drawback will disappear because the carbonate of li1ne does not decompose the sulfate of zinc, and the reaction commences only in the presence of sulfurous acid. This reaction however liberates the carbonic acid so that in order to avoid a rise of pressure in the apparatus, it is necessary to blow off gas at frequent intervals which gas carries away with it not only the carbonic acid but also a suitable proportion of sulfurous'acid can act successively 1n a cycle, and to this solution while being agitated there is added the anhydrous or hydrated-earthy alkaline oxid', care being taken that-the added quantity of oxid shall always be less than that which is necessary for fixing approximately half of the dissolved sulfurous acid, in the form of earthy alkaline sulfite.

By way of'example there will now be described the treatment of a solution of zinc sulfate with barium oxid. Under these conditions the barium oxid is at once converted into sulfite and the sulfite thus formed reacts at once upon the zinc sulfate so as to produce by double decomposition barium sulfate and zinc sulfite, which latter remains in solution owing to the excess of sulfurous acid By regulating the introduction of the sulfurous acid and the barium oxid so as to 'always keep to the above stated proportions,

- the preceding three reactions will take place simultaneously" without any disturbance, and he whole of the zinc will remain entirely in lution. These reactions can be readily -arried into practice onthe manufacturing scale by means of suitably adjusted dosing devices. Since the flow of sulfurous acid is continuous the sulfite of zinc will remain in solution owing to the excess of sulfurous acid"; while the barium sulfate will be pre cipitated in the. densest form resulting from the double decomposition between two salts. After filtering the solution'for'the purpose of separating out the sulfate5'the sulfite solntion is treated by any suitablemeans for 'the purpose of eliminating therefrom the sulfurous acid in excess and allowing of the precipitation of the zinc sulfite. This zinc s ulfite when calcined will furnish the oxid while regenerating the sulfurous acid which on being added to the aforesaid quantity allows of restarting theworking cycle. The barium sulfate when treated by ordinary means. will regenerate the baryta which is employed in the first stage of the process. Thus by using suitable proportions of S111- furous acid and the earthy alkaline base, the operator is enabled to control the reactions in the very midst of the solution of zinc salt-s,

continuously through 1'. The process of treating solutions containing sulfate of zinc, consisting in maintaming the zinc solutions saturated with sulfurous acid while adding gradually to the zinc solution duringthe treatment with 'sul-.

furous acid earthy alkaline oxid whereby the zinc sulfite formed is maintained in so lution. v I

2. The processof treating solutions containing sulfate of zinc, consistingi-n maintaining in the zinc'solutions an excess of sulfurous acid while adding to the zinc solution during the treatment with sulfurous acid earthy alkaline oXid substantially as and for the purpose set, forth.

3. The process of treating solutions ,containing sulfate of zinc, consisting in passing continuously through the zinc solution sulfurous acid while adding to the zinc solution during thetreatment with sulfurous acid earthy alkaline oxids, the addition of the alkaline oxid being such that it is always less in quantity-than the quantity which is necessary for fixingv in the formof sulfite abouthalf of the dissolved sulfurous acid.

4. The process"-of-treating solutions con-. consisting injpassing,

taining sulfate ofzinc the zinc solution,- sulfurous acid under pressure5-while adding to the zinc solution earthy alkaline' oxid, the addition of the alkaline oxid being such that it is always less in quantity than the quantity which is necessary for fixing the form of sulfite'substantially half of the dissolved.

sulfurous acid. I v

In testimony whereof I have hereunto set my hand, at Paris of June, 1914.

- ROBERT LANCE. In the presence of two witnesses:

' CHAS. P. Punsspr,

LOUIS CooUrLLA'r,

(France); this tenth day 

